The invention relates to a process for producing sandwich structures from fiber-reinforced ceramics.
Sandwich structures which are composed of a honeycomb core and facings are preferably used as light structural members of high rigidity. Up to now, the base materials for their production usually have comprised metals and plastics, which do not have sufficient resistance to temperatures for special applications, for example, for use in space.
It is an object of the invention to provide a process for producing a structural member which has good physical properties and is highly resistant to increased temperatures (T&gt;700.degree. C.), corrosion and oxidation.
According to the invention, this object is achieved by means of a process including the steps of: impregnating inorganic fibers or a woven material with a slip of Si-organic polymers and a ceramic or metallic powder, molding of facings and honeycomb core by means of winding and laminating techniques, pressure and temperature treatment of facings and honeycomb core for cross-linking (curing) of the organic polymer, joining of the complete structure by aforementioned cross-linking and/or by additional binding agents after the cross-linking, and no-pressure pyrolysis for the conversion into a ceramic material.
For producing the honeycomb core and the facing, inorganic fibers on a base of SiO.sub.2, Al.sub.2 O.sub.3, C, SiC (such as NEXTEL-Fibers, TYRANNO-Fibers, NICALON-Fibers, C-Fibers) are impregnated with a slip of Si-organic polymers (such as silanes, silazanes and/or siloxanes) which are mixed with a ceramic or metallic powder (such as SiC, Al.sub.2 O.sub.3, mullite, Si.sub.3 N.sub.4, glass or SiO.sub.2, metals). The part of the ceramic or metallic powder preferably amounts to 10-70% by volume, and the particle size of the powder is in the range of under 20 .mu.m. The fiber part amounts to approximately 20 to 80% of the total volume of the structural member.